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I have the following query which is intended to retrieve the newest 3 comments for each post in an array of posts.

SELECT * FROM comment AS tbl WHERE sscm_id IN
(
SELECT sscm_id FROM comment AS t1 WHERE t1.sscm_oid = 4
ORDER BY t1.sscm_id DESC LIMIT 3
UNION ALL
SELECT sscm_id FROM comment AS t2 WHERE t2.sscm_oid = 3
ORDER BY t2.sscm_id DESC LIMIT 3
)

which gives me the following error:

1221 - Incorrect usage of UNION and ORDER BY

Some searching & googling seemed to suggest that placing () around each subquery might solve this problem but changing the query to

SELECT * FROM comment AS tbl WHERE sscm_id IN
(
(SELECT sscm_id FROM comment AS t1 WHERE t1.sscm_oid = 4
ORDER BY t1.sscm_id DESC LIMIT 3)
UNION ALL
(SELECT sscm_id FROM comment AS t2 WHERE t2.sscm_oid = 3
ORDER BY t2.sscm_id DESC LIMIT 3)
)

but this gives me the following error:

1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UNION ALL (SELECT sscm_id FROM bpsocial_comment AS t2 WHERE t2.sscm_oid = 3 OR' at line 4

So: how can I get the UNION in combination with the ORDER BY in the subqueries to work?